Tomcat + Apache + Cocoon Performance bottleneck. How to find out the bottleneck is on Apache or tomcat or Cocoon? What can we do to improve the performance?

Additional information
An web application is on E450 with 4x450Mhz CPU, 2GB RAM, Solaris 2.7, with Apache, Tomcat 3.2.2, and Cocoon. The response time is slow when there are more than 40 users at the same time.
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The best way to find out bottlenecks is still using a probling software like JProbe or OptimizeIt!.
Another thing you can do is take Apache out of the picture and test your environment with Tomcat and Cocoon. That will tell you if the problem is in the Apache-Tomcat communication, but I would exclude this.
Regards.